Tube with reservoir of phase change material for an evaporator, associated evaporator and air conditioning assembly

ABSTRACT

The invention relates to a tube ( 1 ) for a heat exchange bundle ( 100 ) of a vehicle heat exchanger, said tube ( 1 ) comprising: —two circulation plates ( 3 ) configured to be assembled together in a sealed manner and to form at least one conduit ( 31 ) in which a first heat transfer fluid circulates between said circulation plates ( 3 ), —at least one reservoir plate ( 5 ) comprising cavities ( 51 ), said reservoir plate ( 5 ) being configured to be assembled in a sealed manner on a face of one of the two circulation plates ( 3 ) so as to close the cavities ( 51 ), the cavities ( 51 ) being projections on the face of the reservoir plate ( 5 ) such that a second heat transfer fluid can circulate between the cavities ( 51 ), the tube ( 1 ) further containing a phase change material stored in the housings formed by the cavities ( 51 ), the phase change material having a solidification temperature between 6 and 8 degrees Celsius.

The present invention relates to a tube having a reservoir of phase change material for a heat-exchange core bundle of a heat exchanger, notably within the field of thermal management within an automotive vehicle.

Heat exchangers generally comprise a core bundle of parallel tubes formed of plates containing a first heat-transfer fluid, for example a refrigerant in the case of an air conditioning circuit evaporator. The core bundle also has passing through it a second heat-transfer fluid, for example a flow of air intended for the vehicle interior, which sweeps over the tubes of which the surface area, increased by the addition of perturbators or inserts between the tubes, optimizes the exchange of heat.

It is known practice to provide these heat exchangers with reservoirs of phase change material which are associated with the tubes of the core bundle used for the circulation of the first heat-transfer fluid. Such exchangers, for example in the case of an evaporator of an air conditioning circuit, allow the cooling of a vehicle interior to be maintained for a given period of time notably when the engine of the vehicle is stopped and no longer driving the compressor that circulates the refrigerant, notably in the case of vehicles fitted with a system that automatically stops the engine when the vehicle is stopped for short periods. During these periods in which the engine is stopped, the phase change material captures heat energy from the air passing through the evaporator so as to cool it.

In particular, there is thus known an evaporator for a vehicle air conditioning circuit, comprising a heat-exchange core bundle provided with a collection of tubes for the circulation of the refrigerant, a reservoir for storing phase change material adjoining the tubes and an air passage being provided between the tubes and the cold-storage reservoirs, notably through the use of protrusions and recesses formed between these two.

However, such air conditioning circuits of relatively high consumers, notably of energy, and the time for which users enjoy thermal comfort is not optimized, notably in the summer and in built-up areas where traffic jams, and therefore vehicle stoppages, are particularly frequent.

It is one of the objects of the present invention to at least partially overcome the disadvantages of the prior art and to propose an improved tube having a reservoir of phase change material for effective use within a heat-exchange core bundle of a heat exchanger.

The present invention therefore relates to a tube for a heat-exchange core bundle of a vehicle heat exchanger, said tube comprising:

-   -   two circulation plates configured to be assembled with one         another in a sealed manner and to form at least one canal in         which a first and heat-transfer fluid circulates between said         circulation plates,     -   at least one reservoir plate comprising cavities, said reservoir         plate being configured to be assembled in a sealed manner on one         face of one of the two circulation plates so as to close the         cavities, said cavities projecting from the face of the         reservoir plate so that a second heat-transfer fluid can         circulate between said cavities,

said tube further comprising a phase change material stored in housings formed by said cavities, said phase change material having a solidification temperature comprised between 6 and 8 degrees Celsius.

Thus, the use of a phase change material exhibiting these characteristics makes it possible to limit the excessive variation in temperature at the outlet of the evaporator and therefore the possibility of cycling in certain components of the air conditioning circuit, such as the compressor, so as to reduce the consumption of the air conditioning circuit.

In other words, the act of using a phase change material having such a solidification temperature leaves open the option of having part of the flow that passes through the air conditioning circuit bypass the evaporator.

In one particular aspect of the invention, the phase change material has a start of solidification temperature comprised between 7.5 and 8 degrees Celsius.

According to one particular aspect of the invention, the phase change material has a melting temperature comprised between 7 and 9 degrees Celsius.

According to one particular of the invention, the phase change material has a latent heat of fusion comprised between 130 kJ/kg·K and 250 kJ/kg·K.

In one embodiment of the invention, the phase change material is a paraffin.

According to an alternative form of the invention, the phase change material is a fatty acid.

The invention also relates to an evaporator for a motor vehicle air conditioning circuit, the evaporator comprising a plurality of tubes according to one of the embodiments set out hereinabove.

The invention further relates to an air conditioning assembly for an automotive vehicle, said assembly having passing through it an air flow, the assembly comprising at least one evaporator according to the invention, the air flow at least partially bypassing the evaporator.

According to one embodiment of the invention, the air flow leaving the evaporator is at a temperature comprised between 1 and 12 degrees Celsius.

The fact that the air flow leaving the evaporator is at a temperature comprised between 1 degree and 12 degrees Celsius makes it possible to have a temperature that is more or less stabilized and therefore render it feasible for the air flow to at least partially bypass the evaporator, therefore reducing the consumption of the air conditioning circuit still further.

Further features and advantages of the invention will become more clearly apparent from reading the following description, given by way of illustrative and nonlimiting examples, and from studying the attached drawings among which:

FIG. 1 shows, in perspective, a schematic depiction of an evaporator according to one embodiment of the invention,

FIG. 2 shows, in perspective, a schematic depiction of a tube having a reservoir of phase change material according to one particular embodiment of the invention, and

FIG. 3 is a graph depicting the state of the phase change material of the invention as a function of its temperature.

In the various figures, identical elements bear the same reference numerals.

As illustrated, the tube having a reservoir of phase change material 1 comprises two circulating plates 3 and at least one reservoir plate 5.

The two circulation plates 3 are configured so that they can be assembled with one another in a sealed manner and to form at least one canal 31 in which a first heat-transfer fluid circulates between said circulation plates 3. The two circulation plates 3 are preferably identical and adjoin one another as “mirror-images” of each other, thereby making it possible to have just one type of circulation plate 3 to be produced, and therefore making it possible to make savings during production.

The at least one reservoir plate 5 itself comprises cavities 51 and is configured to be assembled in a sealed manner on one face of one of the two circulation plates 3 so as to close the cavities 51 and form housings for the phase change material. These cavities 51 project on one face of the reservoir plate 5 so that a second heat-transfer fluid, for example a flow of air, can circulate between said cavities 51.

In the embodiment illustrated, the reservoir plate is assembled on an external face of one of the two circulation plates.

However, other embodiments could be conceived in which the reservoir plate was produced differently and fixed to a different face.

In order to create the tube having a reservoir of phase change material 1 there are just two different types of plates used, namely two circulation plates 3 and at least one reservoir plate 5. Such a design makes it possible to confine the production of such a reservoir tube to these two types of plate, thereby leading to savings in production costs. In addition, because of this reduced number of plate types, assembly is simplified.

An additional advantage of the tube having a reservoir of phase change material 1 is that the phase change material is directly in contact with the circulation plate 3, thereby facilitating and improving the exchanges of heat energy between the first heat-transfer fluid and the phase change material.

The circulation plates 3 may also comprise recesses 32 preferably produced by chasing in a uniform distribution over the entirety of the circulation plate 3. The circulation plates 3 comprise an external face intended to face either toward a reservoir plate 5 or toward an element for exchange of heat with the second heat-transfer fluid, such as a corrugated plate. Each circulation plate 3 comprises an internal face opposite to the external face from which each recess 32 extends so that their top parts are in contact with the adjacent circulation plate 3. According to one preferred but nonlimiting embodiment, the recesses 32 are distributed in a staggered configuration on the circulation plate 3. Because of such a distribution, the interior face of each recess 32 lies in the flow path of the first fluid which passes delimited by the canal 31, whereas the exterior face may form a local reservoir of phase change material, thereby increasing their heat exchange.

Because of the fact that the external face of the circulation plate 3 is provided with recesses 32, these form additional reservoirs of phase change material so that, for a given bulk, a tube having a reservoir 5 of phase change material and provided with such recesses 32 allows increased storage of phase change material. This has the effect of increasing the time for which the phase change material exchanges heat energy with the second fluid.

Furthermore, bearing in mind the fact that the recesses 32 form additional connections of the adjacent circulation plate 3, the mechanical integrity of the tube having a reservoir of phase change material 1 is increased. As a result, such a tube having a reservoir of phase change material 1 can be used in a heat exchanger of the evaporator type which is able to retrieve a refrigerant the pressure of which has a nominal value of approximately 15 bar.

In this embodiment, the tube having a reservoir of phase change material 1 comprises a single reservoir plate 5, on one of its external faces in contact with the second heat-transfer fluid. The other of its faces is in contact with a corrugated plate for exchange of heat with the second heat-transfer fluid, such a corrugated plate sometimes being termed a fin or an insert.

According to an alternative form of the embodiment, the tube 1 may nevertheless comprise a reservoir plate having a reservoir of phase change material 1 on each of its external faces in contact with the second heat-transfer fluid. In order to facilitate the filling of the projecting cavities 51 in this embodiment, the tube having a reservoir of phase change material 1 may comprise a common filling orifice for the projecting cavities 51 of the two reservoir plates 5.

According to one embodiment, the projecting cavities 51 have a domed shape. These domes are more particularly positioned in a staggered configuration so that the second heat-transfer fluid can circulate between them.

According to another embodiment, the projecting cavities 51 have an oblong shape. The projecting cavities 51 are then distributed in a “V” with respect to the longitudinal axis A of the reservoir plate 5, as shown in FIG. 6. This shape and this particular distribution allow the tube having a reservoir of phase change material 1 to contain a greater quantity of phase change material than for the dome shape and also make it possible to limit the head losses of the second heat-transfer fluid as it passes between the projecting cavities 51.

The exchange tube 30 may be a tube provided with microchannels, such a tube being obtained from the superposition of flat plates and of a corrugated plate, the latter sometimes being termed an internal insert, said corrugated plate then being positioned between the two adjacent flat plates in order to form the microchannels.

According to an alternative form of the embodiment, the exchange tube 30 may more particularly be made up of two circulation plates 3, as described hereinabove, assembled with one another in a sealed fashion.

The heat exchange core bundle 100 here comprises, distributed over its entire length, three tubes having a reservoir of phase change material 1. Two of these tubes having a reservoir of phase change material 1 comprise a reservoir plate 5 on each of their external faces in contact with the second heat-transfer fluid. The third tube having a reservoir of phase change material 1 itself has just one reservoir plate 5 on one of its external faces in contact with the second heat-transfer fluid. The total number of tubes having a reservoir of phase change material 1 and of reservoir plates 5 present within a heat-exchange core bundle 100 is dependent on its size and length. The longer the heat-exchange core bundle 100, the higher this number in order to achieve continuous cooling of the second heat-transfer fluid, even if the first heat-transfer fluid is no longer circulating through said core bundle, for example when the compressor is stopped.

Thus, it may be clearly seen that the tube having a reservoir of phase change material 1, because it is made up of two circulation plates 3 and of at least one reservoir plate 5, allows for simple assembly and inexpensive manufacture. In addition, the phase change material is directly in contact with the circulation plate 3, thereby facilitating and improving exchanges of heat energy between the first heat-transfer fluid and the phase change material.

According to the invention, the phase change material chosen is one for which the melting temperature is lowered so as to allow part of the air flow to bypass the evaporator. This bypassing makes it possible to reduce the consumption of the air conditioning circuit overall.

In the mode of operation chosen in this embodiment, the temperature of the air flow leaving the evaporator needs to be comprised between 4 degrees Celsius and 12 degrees Celsius. However, the saturation temperature for the heat-transfer fluid conventionally used lies at around 0 degrees Celsius.

As a result, it is necessary to define a phase change material solidification temperature that is high enough to be compatible with the temperature of the heat-transfer fluid when the entirety of the air conditioning system is in operation, and low enough that the phase change material has liquefied before the temperature of the air flow reaches 12 degrees Celsius.

Thus, and as more particularly illustrated in the graph of FIG. 3 with the curve A which represents the melting of the phase change material and the curve B that represents the solidification of the phase change material, the phase change material can be chosen according to a number of factors.

According to the invention, the phase change material therefore has a solidification temperature comprised between 6 and 8 degrees Celsius.

According to one particular embodiment, it is also possible to employ a phase change material which has a melting temperature comprised between 7 and 9 degrees Celsius.

In one particular embodiment of the invention, which corresponds to the embodiment detailed here, the phase change material has a latent heat of fusion comprised between 130 kJ/kg·K and 250 kJ/kg·K.

As a choice of phase change material, it is possible for example to choose a paraffin.

It is also possible to choose a phase change material from among the fatty acids.

This phase change material may for example be made up of an ester, such as tetradecanoic acid methylethyl ester. In an alternative, it may be made up of 99% tetradecanoic acid methylethyl ester, with one or more additives added to it.

It should be noted that the solidification of the phase change material may preferably occur during a vehicle braking phase, this being rendered possible by increasing the cylinder capacity of a compressor, because the consumption of such a compressor is zero during a braking phase and a braking phase often precedes a phase in which the vehicle is stopped.

This motor vehicle air conditioning assembly, through which a flow of air passes, may comprise, in addition to the evaporator, a compressor and a circuit of flaps operated within a full air conditioning device.

The presence of the compressor means that the air flow at least partially bypasses the evaporator. It should be noted that the air flow leaving the evaporator is at a temperature comprised between 1 and 12 degrees Celsius. 

1. A tube for a heat-exchange core bundle of a vehicle heat exchanger, said tube comprising: two circulation plates configured to be assembled with one another in a sealed manner and to form at least one canal in which a first heat-transfer fluid circulates between said circulation plates; at least one reservoir plate comprising cavities, said reservoir plate being configured to be assembled in a sealed manner on one face of one of the two circulation plates so as to close the cavities, said cavities projecting from the face of the reservoir plate so that a second heat-transfer fluid can circulate between said cavities, a phase change material stored in housings formed by said cavities (51), said phase change material having a solidification temperature comprised between 6 and 8 degrees Celsius.
 2. The tube as claimed in claim 1, the phase change material having a start of solidification temperature comprised between 7.5 and 8 degrees Celsius.
 3. The tube as claimed in claim 1, the phase change material having a melting temperature comprised between 7 and 9 degrees Celsius.
 4. The tube as claimed in claim 1, the phase change material having a latent heat of fusion comprised between 130 kJ/kg·K and 250 kJ/kg·K.
 5. The tube as claimed in claim 1, the phase change material being a paraffin.
 6. The tube as claimed in claim 1, the phase change material being a fatty acid.
 7. An evaporator for a motor vehicle air conditioning circuit, the evaporator comprising: a plurality of tubes for a heat-exchange core bundle, each of the plurality of tubes having: two circulation plates configured to be assembled with one another in a sealed manner and to form at least one canal in which a first heat-transfer fluid circulates between said circulation plates, at least one reservoir plate comprising cavities, said reservoir plate being configured to be assembled in a sealed manner on one face of one of the two circulation plates so as to close the cavities, said cavities projecting from the face of the reservoir plate so that a second heat-transfer fluid can circulate between said cavities, and a phase change material stored in housings formed by said cavities, said phase change material having a solidification temperature comprised between 6 and 8 degrees Celsius.
 8. An air conditioning assembly for an automotive vehicle, said assembly having passing through it an air flow, the air conditioning assembly comprising: at least one evaporator comprising a plurality of tubes, wherein the air flow at least partially bypasses the evaporator, and wherein each of the plurality of tubes comprises: two circulation plates configured to be assembled with one another in a sealed manner and to form at least one canal in which a first heat-transfer fluid circulates between said circulation plates, at least one reservoir plate comprising cavities, said reservoir plate being configured to be assembled in a sealed manner on one face of one of the two circulation plates so as to close the cavities, said cavities projecting from the face of the reservoir plate so that a second heat-transfer fluid can circulate between said cavities, and a phase change material stored in housings formed by said cavities, said phase change material having a solidification temperature comprised between 6 and 8 degrees Celsius.
 9. The air conditioning assembly as claimed in claim 8, the air flow leaving the evaporator being at a temperature comprised between 1 and 12 degrees Celsius. 